The present invention relates to a dental handpiece, in particular a dental handpiece having angular contact ball bearings.
Conventional dental handpieces having angular contact ball bearings have a general structure as shown in FIG. 3, in which head housing 11 accommodates burr sleeve 13, rotor 16, and ball bearings 34, 35. The burr sleeve 13 detachably holds a dental treatment tool 9 therein, and is rotatably supported by the upper and lower bearings 34, 35. The rotor 16 is fixed to the burr sleeve 13 between the upper and lower ball bearings 34, 35, and rotated by compressed air for rotatably driving the burr sleeve 13. The head housing 11 is capped with head cap 18, which is provided with spring 17 and push button 19, and screwed into the head housing 11.
The upper and lower bearings 34, 35 are of the angular contact type, wherein the groove on the outer rings 34b, 35b, i.e. the outer race, is tapered or angled. To each of the outer rings 34b, 35b is attached shield cover 37 using retaining ring 36 for preventing dust, such as debris, from intruding into the bearing. A plurality of balls 34c, 35c are supported at regular circumferential intervals by bearing cages 34d, 35d. The bearing cages 34d, 35d are in the form of a ring having a plurality of pockets 34e, 35e for supporting the balls 34c, 35c therein, as shown in FIGS. 4(a) and 4(b) in side and cross sectional views, respectively.
In the conventional dental handpieces as discussed above, the shield covers 37 interposed between the inner 34a, 35a and outer rings 34b, 35b restrict the spaces available for the bearing cages 34d, 35d. In order to be adapted to this restricted spaces, portions 34dxe2x80x2, 35dxe2x80x2(FIGS. 4(a) and 4(b)) of the cages 34d, 35d facing to the shield covers 37 have to be made smaller, resulting in difference in size between the portions above and below the pockets 34e, 35e of the bearing cages 34d, 35d. 
Due to such asymmetry, when the burr sleeve 13 is rotated, the bearing cages 34d, 35d become unstable and contact the balls 34c, 35c, rattling up and down. This causes abrasion and wearing of the balls 34c, 35c and bearing cages 34d, 35d to damage these parts, and also causes undesirable shaking of the handpiece to generate uncomfortable noise.
The asymmetrical bearing cages 34d, 35d also add to the manufacturing cost of the dental handpiece. In automated assembly of the ball bearings 34, 35, the orientation of the retainers 34d, 35d has to be adjusted as predetermined by the vertically asymmetrical nature of the bearing cages 34d, 35d, which requires special systems and steps.
The present invention has been made to overcome these drawbacks of the conventional dental handpieces. It is therefore an object of the present invention to provide a dental handpiece wherein abrasion and wearing the balls and bearing cages in ball bearings are minimized.
It is another object of the present invention to provide a dental handpiece of which manufacturing cost is suppressed.
It is another object of the present invention to provide a dental handpiece having angular contact ball bearing wherein intrusion of duct into the bearings are effectively prevented.
According to the present invention, there is provided a dental handpiece comprising:
a burr sleeve for detachably holding a dental treatment tool therein;
upper and lower ball bearings for rotatably supporting said burr sleeve;
a rotor fixed to said burr sleeve between said upper and lower ball bearings and rotated by compressed air for rotatably driving said burr sleeve; and
a dust controller including a rotary protruding member fixed on an outer surface of said burr sleeve and rotating integrally with said burr sleeve, and a stationary protruding member attached to a stationary part of said handpiece and having a surface facing to said rotary protruding member to define a gap therebetween, said gap being located outside of said lower ball bearing;
wherein said upper and lower ball bearings are angular contact ball bearings each having a bearing cage, said bearing cage having apertures for supporting balls of said ball bearings therein, said apertures being located substantially in the middle of said bearing cage in a thrust direction.
According to one aspect of the present invention, the conventional shield cover interposed between the inner and outer rings of a ball bearing of conventional dental handpieces is dispensed with, and instead a dust controller is placed outside of the ball bearing to expand the space between the inner and outer rings available for a bearing cage. This expanded space allows a vertically symmetrical bearing cage, i.e., a bearing cage having ball pockets substantially in the middle in the thrust direction, to be disposed between the inner and outer rings of the bearing. This vertically symmetrical bearing cage exhibits improved stability upon rotation of the burr sleeve, and thus minimizes shaking and noise of the handpiece. Further, use of the vertically symmetrical bearing cage eliminates special systems and steps for adjusting the vertical orientation of the bearing cage in automated assembly of the ball bearings, which reduces manufacturing cost of the handpiece.
According to another aspect of the present invention, a dental handpiece having an air turbine wherein a burr sleeve is rotated with compressed air, is provided with a dust controller including a rotary protruding member and a stationary protruding member. The rotary protruding member is fixed on and protrudes from the outer surface of the burr sleeve, and is rotated integrally therewith. The stationary protruding member is attached to and protrudes from a stationary part of the handpiece, and has a surface facing to the rotary protruding member to define a gap therebetween. The gap is located outside of the ball bearing.
The interior of the lower ball bearing communicates with the outside of the head housing via the dust controller. Rotation of the dust controller creates a high-pressure region between the rotation space of the rotor and the outside of the head housing. This high pressure region effectively blocks off air flow out of the head housing, and prevents suction of debris, saliva, blood, and the like through the lower end of the head housing upon stopping of the rotation of the rotor, which creates negative pressure in the head housing during rotation.
In the present invention, the stationary protruding member may be of any shape and configuration, as long as it does not narrow the space between the inner and outer rings of the ball bearing, and has a surface facing to the rotary protruding member to define a gap therebetween, which gap is located outside of the lower ball bearing. For example, the stationary protruding member may be generally in the form of an annular ring, of which radially outer end portion is fixed to the outer ring of the ball bearing, and of which radially inner end portion is extended radially inwardly beyond the inner ring of the ball bearing and defines a surface that faces to the rotary protruding member with a gap formed therebetween. The stationary protruding member may be attached to any stationary part of the handpiece, for example, to the outer ring of the ball bearing.